1. Field of the Invention
The present invention relates to a process and a heating device for thermoforming the interior of a boot having a rigid external upper.
2. Description of Background and Relevant Information
Indeed, such boots, for example, ski boots, or mountain boots, ice skate boots, in-line roller skate boots, etc., must comprise an external upper generally constituted by a shell made out of a rigid plastic material, but which could also be made of thick and rigid leather for mountain boots, for example. Such upper must hold the foot-ankle assembly and, in particular, prevent twisting of the ankle and enable a proper transmission of the forces exerted by the foot, either for steering the ski or the gliding board, or for tilting stability when hill-walking.
Such uppers are thus more or less rigid and, therefore, very uncomfortable.
To improve the comfort of such boots, they must comprise an internal fitting generally constituted by a removable liner and made of more flexible materials such as foams.
Such internal fittings are provided to envelop a certain type of foot. Unfortunately, everyone's foot is more or less different from the "standard" foot which led to the construction of the internal fitting. Because the rigid external upper of the boot cannot deform, painful friction points are often created for the user's foot, regardless of the flexibility of the internal fitting.
To remedy these drawbacks, it is known, especially for the ski boot, to make the internal fitting out of a thermoformable material such as polyethylene which, once brought to a temperature of about 120.degree.-140.degree. C., can be configured according to the user's foot and to the external shell, until it perfectly assumes the shape of the user's foot.
Such a process is described, for example, in EP 004 829. This patent teaches to heat the internal fitting, by means of an electrical circuit incorporated therein, after the foot has been positioned inside the boot. Such a process has practically proven unrealistic and very expensive.
Other solutions proposed by JP 246 876, for example, consist of heating the internal fitting after removing it from the boot, either simultaneously from the inside and outside after placing it in an appropriate heating enclosure, or only from the outside, until it reaches the desired uniform thermoforming temperature, on the order of 120.degree.-140.degree. C.
These solutions are not satisfactory either, because they have numerous drawbacks:
need of providing a cumbersome and costly heating enclosure; PA1 need of manipulating the internal fitting to remove it and reposition it within the boot; PA1 risk of burning when manipulating the internal fitting brought beyond 120.degree. C., and when repositioning it within the boot; PA1 heat loss during these manipulations of the internal fitting which require reheating the fitting; PA1 risk of inverting the left/right internal fittings when repositioning in the boot; PA1 length of the process, because only one fitting can be adapted at a time due to the necessary manipulations. PA1 sending hot air, at a temperature comprised between 120.degree. and 140.degree. C., on at least said portion of the fitting arranged within the boot; PA1 guaranteeing at the same time a predetermined minimum distance between each exit of hot air and said portion of the fitting. PA1 Indeed, this process enables a very simple and very quick implementation due to the fact that it does not require any manipulation of removing or inserting the internal fitting within the boot. It is further compatible with a fitting fixed inside the boot. Finally, it has been noted, in a manner that is not obvious a priory, that the direct heating of the fitting arranged inside the boot did not run the risk of damaging or softening the rigid external upper of the boot, since the temperature obtained on the outside of this fitting does in fact not exceed 80.degree. C. for a thermoforming temperature on the order of 130.degree. C. PA1 at least one hot air distribution nozzle capable of being introduced inside each boot provided with its internal fitting; PA1 means for positioning the nozzle within the boot.
Furthermore, it is neither conceivable to place the boot assembly within the heating enclosure because, on the one hand, the materials constituting the rigid external upper would run the risk of being damaged by the heat and, on the other hand, this external upper would loose its rigidity properties under the effect of such heat, and the thermoforming of the internal fitting would then no longer be justified.
It is also known to use heating apparatuses that are generally constituted by a pipe sending hot air within the ski boots, in order to dry them or reheat them slightly before use. Such apparatuses are not designed for a temperature above 40.degree. and could not be applied directly to a thermoforming of internal fittings at a temperature on the order of 120.degree.-140.degree. C. without risks of damaging the latter.